1. Field of the Invention
This invention relates to a method for continuously excavating the ground and continuously withdrawing the excavated earth to the ground surface in a vertical earth excavation and withdrawal work, particularly large-scale pit digging work, and an apparatus for practicing such a method.
2. Description of the Prior Art
Heretofore, bucket elevators have been prevalently used for vertically conveying dug-out earth to the ground surface in ground excavation work. In bucket elevators of this type a lower earth loading mechanism, a vertical conveying mechanism and an upper earth discharging mechanism are usually assembled into an integral structure with steel frames and other means, and the structure is installed at the site of excavation. In operation, the dug-out earth is first loaded onto the lower earth loading mechanism, then continuously conveyed up to the ground surface by a series of buckets mounted at given intervals on circulating endless chains and thence discharged out through the upper earth discharging mechanism. If the ground excavation is carried out horizontally along a fixed depth, as in the case of underground railway construction or sewage construction, the conventional vertical conveyor system can be used for continuous operation without remodeling said system, but if the ground is dug down to a great depth as in the case of foundation works for a massive building or structure, the vertical conveying mechanism must be extended by adding to the lower portion thereof according to the depth and also the lower earth loading mechanism must be lowered accordingly. Such an adding or extending operation has been generally practiced in the following way: the vertical conveying mechanism is temporarily hoisted up and the lower earth loading mechanism is removed and placed at a separate location, and after effecting the desired addition to the vertical conveying mechanism, the lower earth loading mechanism is re-mounted thereto. Such an adding operation, however, requires a great deal of labor and also necessitates interruption of the excavation work for a long time, resulting in a huge increase in construction cost.